FIG. 5 is a cross-sectional drawing showing a discharging electrode of a conventional transverse discharge excitation pulse laser oscillator apparatus shown for example in DOE/SF/ 90024-T2 (1977) wherein: (1) is a first main electrode; (1a) is a 1/4 inch outer diameter tube which constitutes a tip part of the main electrode (1); (2) is a second main electrode; (3) is a main discharge which is produced between main discharge (1) and (2); (4) is an auxiliary electrode comprised of a wire disposed in the vicinity of the first main electrode (1); (5) is a dielectric material pipe comprised of quartz pipe of approximately 5 mm outer diameter which is disposed in a manner that it contains thee auxiliary electrode (4) inside and contacts the first main electrode (1); (6a) and (6b) are corona discharges taking place on the surface of the dielectric material pipe; and (7a) and (7b) are corona discharge starting points.
Next, explanation is given on its action. First, upon applying a voltage across the first main electrode (1) and the auxiliary electrode (4), corona discharges (6a) and (6b) start from a points (7a) and (7b) at which dielectric material (5) and the first main electrode (1) contact each other in a manner that they cover the dielectric material pipe (5). Ultra-violet radiation is radiated from these corona discharges (6a) and (6b), thereby laser gas existing between the main electrodes (1) and (2) is pre-ionized. Subsequently, when a voltage is applied across the main electrodes (1) and (2), pre-ionized gas starts to discharge and then the main discharge (3) takes place. The laser gas is excited by this main discharge (3), thereby the laser starts to oscillate in a direction which is perpendicular with respect to the plane of sheet. Since the conventional transverse discharge excitation pulse laser oscillator apparatus is constituted as has been described above, there has been a problem that the ultra-violet radiation taking place in the vicinity of the corona discharge starting points (7a) and (7b), at which light emission caused by the corona discharge was strong, was not radiated efficiently into the space between the main discharge electrodes (1) and (2).